1. Field of the Invention
The present invention relates to an imaging device. To be more specific, the present invention relates to image data processing to be performed on an output signal from a color image sensor in order to obtain a high quality image.
2. Description of the Related Art
When shooting by a video camera or an electronic camera, there are cases where line crawling (line-shaped or grid-like noise) occurs in an image. A cause of the occurrence of the line crawling is fixed pattern noise, such as difference in the sensitivity of each pixel, difference in the output level of each vertical transfer line and the like in a color image sensor. A method for smoothing the image is known as a conventional art for making the line crawling inconspicuous. A low pass filter (hereinafter abbreviated as LPF) and the like are used in this smoothing processing (for example, refer to pages 539-548 of “Image Analysis Handbook” written by Mikio Takagi, supervising editor Haruhisa Shimoda, published by University of Tokyo Press on Jan. 17, 1991).
By the way, in many cases, shot image data is subjected to sharpness enhancing processing such as unsharp masking and the like, in order to increase its sharpness and graininess. This sharpness enhancing processing also emphasizes line crawling, which is supposed to be made inconspicuous. Thus, when the line crawling occurs in original image data, it is necessary that original image data be subjected to the smoothing processing such as LPF before being subjected to the sharpness enhancing processing, in order to reduce the line crawling. It is difficult, however, to effectively subject image data to the sharpness enhancing processing after being smoothed. Therefore, it is difficult to obtain a fine image with sharpness from original image data with the line crawling.